The purpose of this study is to treat patients with recurrent malignant gliomas using continuous infusion phenylacetate acid at a dose of 400 mg/kg/day for fourteen days every two weeks. The study endpoints are toxicity, response rates, and time to treatment failure. All patients will be followed for survival. Sufficient accrual will occur to determine if phenylacetate, using this dose schedule, produces a true response or stabilization rate of greater than 20%, as well as improvement in time to progression.